10 August 2017

Legionella flushing regime


The genus Legionella is a pathogenic (disease causing) group of bacteria. The Legionella species L. pneumophila causes legionellosis - a collective term for the diseases caused by the bacteria. Mixer valve showers are a common source of Legionella bacteria and are ultimately responsible for a significant proportion of Legionnaire’s disease outbreaks.


The conditions of a shower often provide the ideal environment for the bacteria to thrive due to factors including:

  • A good supply of nutrients (often in the form of biofilm lining pipes, fittings etc.)
  • Stagnant water at ideal temperatures

To reduce the risk of Legionella growth, consider a flushing regime

Legionella risk can be managed. A fundamental component of managing risk is a flushing regime (running water through the system at high temperatures).  To effectively carry out flushing, “dead legs” and “ends” in pipe work should be removed and outlets (not in regular use) should be flushed weekly or more – this includes taps as well as showerheads.  It is also advised that shower heads and taps are de-scaled quarterly and cold water tanks cleaned periodically.

Factors to be aware of during flushing: 

  • Water should flow through the outlet for 5 minutes or more
  • Flushing should be carried out after cleaning the facility
  • Water should be set at the highest temperature
  • A record should be kept detailing the date of each flushing and who it was carried out by
  • Training should be provided for those responsible for flushing

In some cases, it is difficult to flush systems regularly due to limited access and resource. As a result, self-purging showers should be considered.

Read information surrounding the provision and implementation of Legionella control – NCH Asia is able to provide risk assessments, analytical services, monitoring and control programs and more.

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